The present invention relates to a process for the preparation of flavouring compositions, more particularly the biogeneration of mixtures containing heterocyclic compounds and having roasty, popcorn-like or bread crust-like notes, and which are usable in foodstuffs, especially in bakery food products.
Heterocyclic compounds are important known flavor constituents in many foods, such as meat and bread. Among these compounds, thiazoles and their derivatives play a key role in roasted flavors.
One of these thiazole derivatives with intense roasty flavor is 2-acetyl-2-thiazoline (2-AT), which was reported first as a volatile constituent of beef broth (see J. Agr. Food Chem. vol. 19, No 5, p. 1014-16, 1971). However, this compound has never been identified in bread or bakery products.
Various methods are already known to prepare 2-AT or similar thiazole compounds by organic synthesis (Recueil, vol. 91, p. 711-28, 1972) or through the Maillard reaction (J. Agr. Food Chem. vol. 43, No 11, p. 2946-50, 1995), which are however not appropriate for obtaining food-grade products.
Therefore, the main purpose of this invention was to provide a new and natural route for obtaining complex mixtures containing heterocyclic compounds, especially thiazole derivatives and more particularly 2-AT and precursors thereof, as well as other flavor ingredients.
A first object of the present invention is thus a process for the preparation of a flavouring composition containing 2-acetyl-2-thiazoline (2-AT), precursors thereof and other odorants, which comprises the bioconversion of a sulfur containing compound and an organic acid or a derivative thereof in presence of a yeast. The reaction mixture can advantageously be then submitted to a separation step, for example by centrifugation, so as to recover the supernatant from the mycelium, this supernatant being usable as a flavouring composition either directly in liquid form or after drying in powder form obtained by mild dehydration methods.
The sulfur-containing compound can be selected from the group comprising the compounds having the following formula (I): 
where
R is H, xe2x80x94COOH, xe2x80x94COOM (M=Na or K), xe2x80x94COONH4, or xe2x80x94COxe2x80x94NHxe2x80x94CH2xe2x80x94COOH,
X is H, HCl, HBr or xe2x80x94COxe2x80x94(CH2)2xe2x80x94CH(NH2)xe2x80x94COOH,
and n is 1 or 2,
as well as peptides including said compounds of formula (I).
Among these compounds, those preferred are cysteamine and cysteine, or the salts and derivatives thereof, as well as glutathione.
As organic acids, those being of food grade such as the hydroxy- or keto-propionic acids, as well as their derivates, esters and salts thereof, can be used, for example lactic or pyruvic acids, or esters thereof such as ethyl-lactate or ethyl-pyruvate.
The preferred yeast used for the bioconversion is baker""s yeast, for example in the form of a powder, an extract or a cream solution, but other kinds of microorganisms can also be used, such as for example Candida versatilis, Debaromyces hansenii, Saccharomyces bayanus, etc. Preferably, the yeast is fresh, up to about 8 days, advantageously up to about 4 days, and kept in the refrigerator.
Regarding the respective quantities of the two starting products, they can be such as the molar ratio between the sulfur-containing compounds and the organic acid is about 1:1 or up to about 1:2. The concentration of these substrates in the reaction medium can be of 1 to 100 mMol, preferably from 10 to 30 mMol.
Generally, the yeast cream solution is used as from 20 to 60 ml per mMol of substrate, but this range can be adjusted according to the yeast and the substrates concerned.
Furthermore, the incubation with yeast can be carried out in presence of a sugar, such as tetroses, pentoses, hexoses, preferably glucose.
Regarding the other reaction conditions, the incubation with the microorganisms is preferably carried out in the activation conditions of the carboxypeptidase enzyme. This can be under aerobic or anaerobic conditions, preferably aerobic during 2 to 72 hr, preferably 4 to 48 hr, and at a pH of 7.0 to 11.0, preferably 8.0 to 10.0. The temperature of the reaction can be of 20 to 50xc2x0 C., preferably 30-40xc2x0 C., and it can be carried out under medium to high agitation conditions.
The reaction medium can be water or a buffer solution, such as phosphate or carbonate-bicarbonate.
As already mentioned, the reaction mixture is advantageously after bioconversion submitted to a separation step, preferably by centrifugation, so as to recover the supernatant from the mycelium. The supernatant can be either maintained as it is in liquid form or converted into a powder using mild conditions, e.g. by spray or freeze drying (with or without maltodextrin, cyclodextrin, modified starch, etc.).
The flavouring composition thus obtained by the process according to the invention revealed a flavour described after sensory evaluation as roasty, meaty, sausage-like, dried sausage-like and somewhat amine-like.
The supernatant obtained by the process according to the invention may also be dried in a vacuum oven at a temperature between 40 and 80xc2x0 C. during 2 to 5 hours, preferably 3 to 4 hours, in order to provide a powder having a more pronounced roasty, popcorn-like and bread crust-like notes.
It has been further suprinsingly found that when the process according to the invention comprises a subsequent step of heat treatment of the flavouring composition obtained, which constitutes another object of the present invention, said composition is transformed into another flavouring composition, which is presenting a different flavour, i.e. with more pronounced roasty, popcorn-like or breadcrust-like notes, and to a lesser extent meaty-like note.
This can be explained by the fact that, under the action of the heating, the concentration of 2-AT is significantly increased (about 10 to 100 times) and that other compounds such as 2-methylthiazolidine, N-acetylcysteamine, 2-methyl-3-furanthiol and 3-mercapto-2-pentanone are fully or at least partially decomposed.
The additional heat treatment can be carried out either directly on the liquid composition as recovered after the bioconversion process, or on the dehydrated powder prepared from said liquid composition, if appropriate in presence of other ingredients.
The preferred conditions of this additional heat treatment, which have been experimentally determined, are the following : 100-250xc2x0 C., 10 to 120 min, and pH comprised between 6 and 10, preferably between 7 and 8.
Also surprisingly, it has been further shown that a flavouring composition presenting such an increased content of 2-AT can advantageously be used in foodstuffs and more particularly in bakery products, so as to improve the roasty, popcorn-like and bread crust-like notes thereof; this constitutes still another object of the present invention.
Furthermore, in the case of the bakery products, the original flavouring composition before heat treatment can be either added to the various constituents and ingredients to be baked (in dough) or applied as a coating for example by pulverizing the liquid composition or spreading the powder form thereof on the prebaked products.